1. Field of Endeavor
The present invention relates to a method for operating a firing plant with at least one combustion chamber and with at least one burner for producing hot gas, especially a gas turbine, preferably in a power generating plant. The invention also relates to a firing plant with at least one combustion chamber and at least one burner for producing hot gas.
2. Brief Description of the Related Art
A firing plant, for example a gas turbine, customarily has at least one combustion chamber with at least one burner. Furthermore, a fuel supply system is always provided, by which the burners are supplied with fuel. With regard to regulations which are becoming ever stricter concerning limiting values which are to be observed for pollutant emissions, it is sought to operate the burners as close as possible to the lean extinction limit. As a result of such a lean operation, especially the creation of harmful NOx emissions can be reduced.
The influencing parameters which determine the extinction limit vary in this case during operation of a gas turbine. Such influencing parameters, for example, are boundary conditions such as the ambient temperature, the relative air humidity, the air mass flow which depends especially upon the operating state of the upstream compressor, and the composition of the fuel which is currently used, etc. The burners, with regard to their fuel feed, are frequently divided into two or more groups so that an influence can be exerted upon the equivalence ratio of the combustion process. In this case, the fuel feed to the two or more burner groups is customarily controlled in dependence upon the aforementioned factors. Since, however, not all important parameters, and especially not all changes to each time point, can be adequately taken into consideration, a predefined fuel staging ratio or burner group staging ratio is always selected with a certain safety margin to the lean extinction limit.
This safety margin is to ensure that even during a change of the individual boundary conditions, which act differently upon the stability of the combustion process, a stable operation of the individual burners is ensured. A stable operating state takes highest priority, especially in the case of power generating plants which are used for electric power generation, so that the safety margin is greater than is absolutely necessary and consequently higher NOx emissions are accepted.